Conventional inflatable sports balls, such as soccer balls, typically have a spherical (or ovoid) outer casing and an inflatable bladder within the casing. Often, one or more intermediate layers are provided between the bladder and the casing to provide additional strength and/or cushioning. The outer casing may itself be a laminate construction for improved strength and durability. The bladder is inflated with air through a valved opening that extends from the bladder to the outer casing.
The outer casing of a conventional soccer ball is formed from a series of leather or synthetic leather (e.g. PU and PVC) panels that are joined to one another along their edges to form the enclosure within which the bladder is retained. The pressure of the inflated bladder within the casing forces the joined panels to assume the desired spherical shape. Various panel configurations are possible but the most common arrangement is a casing that includes twenty regular hexagonal panels and twelve regular pentagon shaped panels arranged in the form of a truncated icosahedron.
The panels are joined at their edges by stitching or with adhesives or by thermally bonding the panel edges to one another.
The highest quality balls tend to be hand-stitched as this tends to give tighter stronger seams, which in turn results in a ball that has good power and aerodynamic properties. Mid-range balls are often also stitched but use machine stitching, which does not tend to produce seams that are as strong as the hand-stitched balls. Lower-end practice balls often use glued seams resulting in balls that typically do not perform as well but have the advantage that they do not take up as much water as stitched seam balls when used in the wet. More recently, thermally bonded balls (in which the panel edges are bonded to one another using heat and by means of an adhesive) have become popular, which offer stronger seams than glued balls. However, thermally bonded balls do not tend to perform as well as a good hand-stitched ball, especially as the seams tend to have relatively flat profiles that are difficult to keep consistent, which can lead to poor aerodynamics.